The present invention relates to an art for purifying exhaust gas discharged from an internal combustion engine installed in a motor vehicle or the like. In an internal combustion engine installed in a motor vehicle or the like, an exhaust gas purification catalyst is disposed in the midst of an exhaust passage for the purpose of purifying noxious gas components in exhaust gas. As an example of such an exhaust gas purification catalyst, there is known a three-way catalyst having a noble metal catalytic substance of platinum-rhodium type carried on a surface of a ceramic carrier coated with alumina. When the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is in the vicinity of a stoichiometric air-fuel ratio, the three-way catalyst causes hydrocarbon (HC) and carbon monoxide (CO) contained in exhaust gas to react with oxygen (O2) in exhaust gas to be oxidized into water (H2O) and carbon dioxide (CO2), and at the same time, causes nitrogen oxides (NOx) contained in exhaust gas to react with hydrocarbon (HC) and carbon monoxide (CO) in exhaust gas to be reduced into water (H2O), carbon dioxide (CO2) and nitrogen (N2).
The three-way catalyst as mentioned above makes it possible to purify the unburnt HC, CO and NOx contained in exhaust gas, whereby those noxious gas components are prevented from being discharged. The three-way catalyst is activated at a temperature equal to or higher than a predetermined activation temperature (e.g. 300to 500xc2x0 C.) and becomes capable of purifying noxious gas components in exhaust gas. However, when the three-way catalyst is at a temperature lower than the activation temperature, it is inactive and thus incapable of purifying noxious components in exhaust gas.
In particular, for example, if the internal combustion engine has been cold-started, the fuel injection amount is increased more than usual for the purpose of enhancing the startability of the internal combustion engine, ensuring driveability and so on. Meanwhile, since the combustion in the internal combustion engine is destabilized, the amount of unburnt fuel components (e.g. HC) contained in exhaust gas is relatively large. In this case, if the three-way catalyst is inactive, there arises an inconvenience in that a relatively large amount of unburnt HC is discharged into the atmosphere without being purified.
To solve such a problem, there is proposed, for example, an engine exhaust gas purifier as disclosed in Japanese Patent Application Laid-Open No. HEI 4-17710. The engine exhaust gas purifier disclosed in this publication includes a bypass passage bypassing part (a main exhaust passage) of an exhaust passage downstream of an exhaust gas purification catalyst, adsorption means installed in the bypass passage, and a flow passage switching valve which allows exhaust gas to pass through the bypass passage only when the exhaust gas is at a low temperature lower than a predetermined temperature and shuts off flow of exhaust gas in the bypass passage upon generation of a signal relating to a sudden change in operational state.
The engine exhaust gas purifier thus constructed blocks the main exhaust passage when the exhaust gas temperature is lower than a predetermined temperature, and at the same time, controls the flow passage switching valve to open the bypass passage, thus causing the unburnt HC that has not been purified in the exhaust gas purification catalyst to be adsorbed by the adsorption means.
When the exhaust gas temperature is equal to or higher than a predetermined temperature, the engine exhaust gas purifier predicts that unburnt HC is discharged from the adsorption means, and opens the main exhaust passage. At the same time, the engine exhaust gas purifier controls the flow passage switching valve so that the bypass passage is shut off, thus preventing the unburnt HC discharged from the adsorption means from being discharged into the atmosphere.
In addition, if the operational state of the internal combustion engine has abruptly changed, for example, into high-load operation when the exhaust gas temperature is equal to or lower than a predetermined temperature, the aforementioned engine exhaust gas purifier opens the main exhaust passage and controls the flow passage switching valve so that the bypass passage is shut off. Thereby unburnt HC is prevented from being desorbed from the adsorption means, and the exhaust gas resistance is reduced.
In the aforementioned engine exhaust gas purifier, since the flow passage switching means is controlled only in consideration of an abrupt change in operational state of the engine and a temperature of exhaust gas, the following inconveniences may arise. For example, the heavier the property of the fuel burnt in the internal combustion engine becomes, the easier it becomes for unburnt HC to adhere to a wall surface of the exhaust passage or the exhaust gas purification catalyst. Hence, it takes a long time until the unburnt HC discharged from the internal combustion engine reaches the adsorbent. Thus, there is a concern that the unburnt HC might be discharged into the atmosphere through the main exhaust passage after flow of exhaust gas through the bypass passage has been blocked.
If the exhaust gas purification catalyst has deteriorated, especially if the low-temperature activation ability of the exhaust gas purification catalyst has deteriorated, it takes a long time until the exhaust gas purification catalyst is activated, and over a long period of time, unburnt HC is discharged from the exhaust gas purification catalyst without being purified. Therefore, there is a concern that unburnt HC might be discharged from the exhaust gas purification catalyst after flow of exhaust gas through the bypass passage has been blocked, and that the unburnt HC might be discharged into the atmosphere through the main exhaust passage.
The present invention has been made in consideration of the aforementioned problems. It is an object of the present invention to effectively utilize the performance of an adsorbent and improve exhaust emission properties, by providing an art for controlling flow passage switching means in accordance with a mode in which unburnt fuel components discharged from an internal combustion engine reach the adsorbent or a mode in which the unburnt fuel components adsorbed by the adsorbent are desorbed from the adsorbent, in an exhaust gas purifier for the internal combustion engine having a main exhaust passage communicating with the internal combustion engine, a bypass passage bypassing the main exhaust passage, the adsorbent disposed in the bypass passage, and the flow passage switching means for switching flow of exhaust gas into the main exhaust passage and the bypass passage.
With a view to solving the aforementioned problem, the present invention has taken the following measure. That is, an exhaust gas purifier for an internal combustion engine includes an exhaust passage connected to the internal combustion engine and partially formed of a main exhaust passage and a bypass passage bypassing the main exhaust passage, an adsorbent which is disposed in the bypass passage and adsorbs unburnt fuel components in exhaust gas, flow passage switching means for switching flow of exhaust gas to the main exhaust passage and the bypass passage, reaching mode prediction means for predicting a mode in which unburnt fuel components reach the adsorbent from the internal combustion engine, and switching control means for controlling the flow passage switching means in accordance with the mode predicted by the reaching mode prediction means.
In the exhaust gas purifier thus constructed, when unburnt fuel components contained in the exhaust gas discharged from the internal combustion engine need to be adsorbed by the adsorbent, the flow passage switching means operates so that the entire exhaust gas discharged from the internal combustion engine flows into the bypass passage. If it becomes unnecessary to cause the unburnt fuel components contained in the exhaust gas discharged from the internal combustion engine to be adsorbed by the adsorbent, the flow passage switching means is switched from the state where the entire exhaust gas flows into the bypass passage, and operates so that the entire exhaust gas or most of the exhaust gas flows into the main exhaust passage.
At this moment, the reaching mode prediction means predicts a mode in which the unburnt fuel components to be adsorbed by the adsorbent reach the adsorbent. The switching control means controls a timing for switching the flow passage switching means based on the mode predicted by the reaching mode prediction means.
That is, the flow passage switching means switches the flow passage after all the unburnt fuel components to be adsorbed by the adsorbent have reached the adsorbent.
Consequently, there is no possibility that the flow passage be switched before all the unburnt fuel components to be adsorbed by the adsorbent reach the adsorbent or that the flow passage be switched with an undue delay after all the unburnt fuel components to be adsorbed by the adsorbent have reached the adsorbent.
The exhaust gas purifier in accordance with the present invention may further include fuel property judgement means for judging a property of fuel burnt in the internal combustion engine, and may be designed so that the reaching mode prediction means predicts a reaching mode of unburnt fuel components using the property of fuel judged by the fuel property judgement means as a parameter.
The reason for employing this construction is as follows. The heavier fuel becomes, the easier it becomes for unburnt fuel components to adhere to the exhaust passage or the like upstream of the adsorbent. Thus, it takes a long time until all the unburnt fuel components to be adsorbed by the adsorbent reach the adsorbent. Therefore, it is necessary to retard the timing for switching the flow passage accordingly.
Also, the exhaust gas purifier in accordance with the present invention may further include exhaust gas purification means disposed in the exhaust passage upstream of the adsorbent to purify at least unburnt fuel components contained in exhaust gas, and deterioration degree judgement means for judging a degree of deterioration of the exhaust gas purification means, and may be designed so that the reaching mode prediction means predicts a reaching mode of unburnt fuel components using the degree of deterioration judged by the deterioration degree judgement means as a parameter.
The reason for employing this construction is as follows. If the low-temperature activation ability of the exhaust gas purification means deteriorates, it takes a long time until the exhaust gas purification means which is at a low temperature and inactive, and over a long period of time, unburnt fuel components are discharged from the exhaust gas purification means without being purified. Therefore, it is necessary to retard the timing for switching the flow passage accordingly.
Next, an exhaust gas purification catalyst in accordance with the present invention may be characterized by including an exhaust passage connected to the internal combustion engine and partially formed of a main exhaust passage and a bypass passage bypassing the main exhaust passage, an adsorbent which is disposed in the bypass passage and adsorbs unburnt fuel components in exhaust gas at a temperature lower than a predetermined temperature, flow passage switching means for switching flow of exhaust gas to the main exhaust passage and the bypass passage, reaching mode prediction means for predicting a mode in which unburnt fuel components reach the adsorbent from the internal combustion engine, desorption mode prediction means for predicting a mode in which the unburnt fuel components adsorbed by the adsorbent are desorbed, and switching control means for controlling the flow passage switching means in accordance with the mode predicted by the reaching mode prediction means and the desorption mode prediction means.
In the exhaust gas purifier thus constructed, when the unburnt fuel components contained in the exhaust gas discharged from the internal combustion engine need to be adsorbed by the adsorbent, the flow passage switching means operates so that the entire exhaust gas discharged from the internal combustion engine flows into the bypass passage. If it becomes unnecessary to cause the unburnt fuel components contained in the exhaust gas discharged from the internal combustion engine to be adsorbed by the adsorbent, or if the unburnt fuel components adsorbed by the adsorbent are desorbed, the flow passage switching means is switched from the state where the entire exhaust gas flows into the bypass passage and operates so that the entire exhaust gas or most of the exhaust gas flows into the main exhaust passage.
The reaching mode prediction means predicts a mode in which the unburnt fuel components to be adsorbed by the adsorbent reach the adsorbent, and the desorption mode prediction means predicts a mode in which the unburnt fuel components adsorbed by the adsorbent are desorbed.
The switching control means controls a timing for switching the flow passage switching means based on the modes predicted by the reaching mode prediction means and the desorption mode prediction means.
That is, the flow passage switching means switches the flow passage when all the unburnt fuel components to be adsorbed by the adsorbent reach the adsorbent, or when the unburnt fuel components adsorbed by the adsorbent start being desorbed.
Consequently, there is no possibility that the flow passage be switched before all the unburnt fuel components to be adsorbed by the adsorbent reach the adsorbent or that the flow passage be switched with an undue delay after all the unburnt fuel components to be adsorbed by the adsorbent have reached the adsorbent.
The desorption mode prediction means may predict the mode in which unburnt fuel components are desorbed, for example, using an amount of intake air in the internal combustion engine or an opening degree of a throttle valve disposed in an intake passage of the internal combustion engine as parameters.
The reason for employing this construction is as follows. If the amount of intake air in the internal combustion engine has abruptly increased, or if the opening degree of the throttle valve has abruptly changed towards the opening direction and caused an abrupt increase in amount of intake air in the internal combustion engine, the amount of exhaust gas discharged from the internal combustion engine increases in accordance with the increase in amount of intake air. Thus, the flow rate and pressure of the exhaust gas passing through the adsorbent increase, and the adsorbent rises in temperature abruptly to such an extent that the unburnt fuel components adsorbed by the adsorbent are desorbed easily.